Japanese Patent Laying-Open No. 2004-289657 (Patent Document 1) discloses a video intercom system connecting one or a plurality of intercom slave units each having a camera to a home network interconnecting a plurality of home electric appliances and household equipment for exchanging data (a general-purpose appliance that cannot be directly connected to the home network is connected via a conversion interface block), characterized in that the intercom slave unit having a camera includes a control unit connected to general-purpose appliances such as a TV set, telephone, and the like via the network.
The invention disclosed in Patent Document 1 can provide flexible system configuration.
Japanese Patent Laying-Open No. 2003-078629 (Patent Document 2) discloses an intercom apparatus, including: an intercom slave unit with a camera, having a call switch used by a visitor to contact a resident, a microphone and a speaker allowing the visitor to speak with the resident, and a camera taking an image of the visitor; an intercom host unit connected with the intercom slave unit with the camera via two nonpolar analog lines and having a display unit displaying the image taken by the camera of the intercom slave unit, a microphone and a speaker allowing the resident to speak with the visitor, a data encoding/decoding unit encoding or decoding video and audio data from the intercom slave unit with the camera, a communication unit simultaneously transmitting and receiving data via a local area network, and a control unit performing data processing, communication control, and the like; and a subhost unit connected with the intercom host unit via two nonpolar analog lines and having a structure similar to the intercom host unit and thus capable of responding to the visitor.
The invention disclosed in Patent Document 2 can provide enhanced installability.    Patent Document 1: Japanese Patent Laying-Open No. 2004-289657    Patent Document 2: Japanese Patent Laying-Open No. 2003-078629